1. Field of the Invention
The present invention pertains to respiratory masks, also commonly referred to as patient interface devices, that are used to deliver a breathing gas to the user, and, in particular, to an engineered surface for such a device that is structured to contact the skin of the user and provide low friction and improved comfort for the user.
2. Description of the Related Art
A variety of respiratory masks are known that have flexible seals and cover the nose, mouth, or both of a human user. The seals, which are also commonly referred to as cushions, are intended to create a seal against the user's face. Because of the sealing effect that is created, gases can be provided at a positive pressure within the mask for delivery to the airway of the user.
The uses for such masks range from high altitude breathing, i.e., aviation applications, to mining and fire fighting applications, to various medical diagnostic and therapeutic applications. For example, such masks are used in the delivery of continuous positive airway pressure (CPAP) or variable airway pressure, such as a bi-level pressure that varies with the user's respiratory cycle or an auto-titrating pressure that varies with the monitored condition of the user. Typical pressure support therapies are provided to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), or congestive heart failure. During use, such respiratory masks, also often referred to as patient interface devices, are strapped on the head of the patient in order to interface the pressure generating device (e.g., a CPAP machine) with the patient.
A requisite of such respiratory masks is that they provide an effective seal against the user's face to prevent leakage of the gas being supplied, while also providing a comfortable user/seal interface. This problem is most crucial because such masks are typically worn for an extended period of time. One concern in such a situation is that a user may avoid wearing an uncomfortable mask, defeating the purpose of the prescribed pressure support therapy.
Surveys have shown that as much as 70% of the population of users of respiratory masks suffers from facial red marks in some form after using a respiratory mask during therapy. The recovery time varies from minutes to hours, but in extreme cases, longer-lasting skin damage and pressure-sores can occur. The root causes of red mark formation are the prolonged pressure and shear loading of the skin by the mask cushion in combination with the build-up of moisture and heat in the skin due to the prolonged occlusion. An important factor in these root causes is skin friction.
Thus, there is a need for a surface for use in a device, such as a respiratory mask, that is structured to contact the skin of the user for prolonged periods that provides reduced friction and/or increased comfort for the user.